1. Field of the Invention
The present invention relates to a surface emitting device and a projection display device using the same, and more particularly, to a surface emitting device and a projection display device, in which high power output can be produced by configuring a large-scaled LED.
2. Discussion of the Related Art
A light emitting diode (LED) is a device that emits light using an electric signal. The LED can be driven at a low voltage such that it is widely in small-sized optical elements. In recent years, the LED is developed as an illuminating light source by increasing its efficiency.
FIG. 1 is a view showing a structure of a conventional LED.
Referring to FIG. 1, a conventional LED includes an n-type layer 12, a light emitting layer 13 and a p-type layer 14, which are sequentially stacked on a substrate 11.
The p-type layer 14 is connected to an anode electrode 15 such that positive voltage is supplied thereto, and the substrate 11 is connected to a cathode electrode 16 such that negative voltage is supplied thereto.
If voltages are applied to the anode electrode 15 and the cathode electrode 16, electrons are moved due to a voltage difference between the anode electrode 15 and the cathode electrode 16. Thus, energy change occurs within the light emitting layer 13 and light is emitted. The light emitted from the light emitting layer 13 is dispersed in all directions. In order to focus the light in one direction, a reflector 7 is provided to reflect the light. The reflected light is condensed by a condenser lens 18.
In such an LED, a single chip or a single module may be used as a light source. However, since the luminous efficiency of the LED is limited, it is difficult to use the single chip or the single module as a high-power light source.
Meanwhile, as shown in FIGS. 2A and 2B, a plurality of LED modules 21 must be arranged in vertical and horizontal directions so as to use the LED as a light source for surface emission.
Since the LED chip has a very small size (several tens of micrometers), a large number of LED chips are required in configuring a surface light source of a predetermined size. Thus, when the LED chip is driven, power consumption is increased.
In addition, it is difficult to make the reflector and the condenser lens with small sizes, gaps 22 in the LED arrangement are wide. Thus, circuit interconnections for connecting the LEDs are complicated. For these reasons, there occur problems in using the LED as the surface light source.
Further, the single LED module has a limit in the power output, and the surface light source configured with the arrangement of the LED modules has many problems. Therefore, it is difficult to adopt the LED as the light source for the illuminating system or the projection display device.